1. Field of the Invention
This invention relates to a dish shaped apparatus and, more particularly, to a collapsible dish shaped apparatus, the surface of which is used, for example, as an antenna to collect or reflect light or radio waves or other forms of electromagnetic energy.
2. Description of the Prior Art
Objects to be sent into space need to be as compact and as light weight as possible. At the same time, it is usually necessary to provide space satellites with antennae which include comparatively large, dish shaped surfaces. Therefore, it is necessary to find a means of compactly packing a dish shaped surface so that it may be assembled after deployment of the satellite in space. It is also desirable to find a means of latching the various parts of the dish shaped surface to one another, after it is assembled, to increase the stability of the structure.
The prior art contains two attempts to resolve this problem. (Holland, U.S. Pat. No. 3,176,303, issued Mar. 30, 1965, and Emde, U.S. Pat. No. 3,618,101, issued Nov. 2, 1971.) The device of Holland achieves compactness by the use of flexible panels. The dish shaped surface is compacted by contracting its circumference, forcing adjacent panels to overlap. The apparatus is held in the compact shape by restraining means, which are released after the satellite is deployed. The natural resilience of the panel material restores the apparatus to approximately its original dish shape.
The device of Holland has three disadvantages. First, by the nature of the flexible materials used for the panels, it is not certain that the original shape of the dish will be exactly restored, when the restraining means are released. Second, the nature of the flexible materials makes it impractical to repeatedly test the assembly and disassembly of the apparatus before launch, since most materials lose their resilience after repeated contraction and release. Third, the means of latching adjacent panels is unsatisfactory, since the Holland device uses shallow depressions containing magnets. The depressions must be shallow, because the expanding panel surfaces slide over each other into their final positions. However, such shallow latching mechanisms provide minimal lateral holding force, i.e. the force necessary to resist so-called "barrel torque."
The Emde device achieves compactness with rigid panels by stacking them sequentially on top of each other. Assembly requires two motions for each panel: first a rotation around a central axis, followed by a vertical motion with respect to that same axis to drop the panel into its place in the final configuration.
The device of Emde avoids the disadvantages associated with panels made of flexible, resilient material. However, the device of Emde still has two disadvantages. First, it shares with the Holland device the disadvantage that the panels slide over each other and therefore it is difficult to provide for a latch that will resist barrel torque. Second, the necessity that each panel move sequentially in two different directions involves an undesirable complexity that is particularly inappropriate for a device usually meant to be assembled automatically.
Attention is also called to Kaminskas, U.S. Pat. No. 4,811,034, issued Mar. 7, 1989, which shows a device which operates in a similar fashion to that of Emde. However, it also shares the disadvantages of the device of Emde.